The present disclosure relates generally to exhaust gas-driven turbochargers. More particularly, the disclosure relates to a turbine assembly of a turbocharger for use with an internal combustion engine having two banks of engine cylinders, each bank having engine cylinders exhausting exhaust gas into an exhaust gas discharge line separate from the exhaust gas discharge line for the other bank.
An exhaust gas-driven turbocharger is a device used in conjunction with an internal combustion engine for increasing the power output of the engine by compressing the air that is delivered to the engine's air intake to be mixed with fuel and burned in the engine. A turbocharger comprises a compressor wheel mounted on one end of a shaft in a compressor housing and a turbine wheel mounted on the other end of the shaft in a turbine housing. Typically the turbine housing is formed separately from the compressor housing, and there is a center housing connected between the turbine and compressor housings for containing bearings for the shaft. The turbine housing defines a generally annular chamber that surrounds the turbine wheel and that receives exhaust gas from the engine. The turbine assembly includes a nozzle that leads from the chamber into the turbine wheel. The exhaust gas flows from the chamber through the nozzle to the turbine wheel and the turbine wheel is driven by the exhaust gas. The turbine thus extracts power from the exhaust gas and drives the compressor. The compressor receives ambient air through an inlet of the compressor housing and the air is compressed by the compressor wheel and is then discharged from the housing to the engine air intake.
Internal combustion engines are not steady-flow devices because each engine cylinder is closed during the compression and combustion/expansion strokes of a full cycle. Thus, the stream of exhaust gas discharged by a given cylinder is actually a series of short bursts or pulses of exhaust gas, each pulse corresponding to the exhaust stroke of a cycle. In engines having multiple cylinders, it is known that it can be advantageous to “gang” the cylinders in two groups or banks, such that the cylinders in one bank exhaust into one exhaust gas discharge line and the cylinders in the other bank exhaust into another separate exhaust gas discharge line. The two lines then feed the exhaust gas to the turbocharger in such a way that the two streams of exhaust gas are kept separate for as long as possible. Such an arrangement can take advantage of the “pulse” effect in the exhaust streams.
In a conventional turbocharger having a single turbine volute, the pulse effect is not optimized, particularly at low gas flow rates, because the two exhaust streams must merge and mix when they enter the turbine housing of the turbocharger. When the exhaust is fed into a single large-volume volute at low flow rates, the pulse energy in the exhaust gas is not efficiently converted into mechanical energy in the turbine.